Process of making molded compositions



Patented Mar. 1,1927.

I UNITED STATES PATENT I OFFICE.

LAWRENCE E. BARRINGER, OF SCHENEC'IADY, AND CHARLES I. PETERSON, OF SCO'IIA, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROCESS OE MAKING MOLDED COMPOSITIONS.

No Drawing. Originalapplication filed September 13, 1922, Serial No. 588,079. Divided and this application filed April 10, 18%, Serial No. 22,213. Renewed July 26, 1026.

The present invention relates to composite insulation containing mica and it is the particular object of our invention to provide mica compositions having improved physical 6 and electrical properties.

The so-called pasted mica consisting of plates or flakes of mica bonded together, has for many years been made by the use of a binder of natural gum, such as shellac or 10 copal. Attempts have been made from time to time to use other binders but none have proved as suitable as shellac. However, shellac softens at comparatively low temperature (about 65 to 70 C.) and decomposes as the temperature increases, decomposition setting in rapidly between 175 and 200 (1., hence certain disadvantages accompany its use.

In assembly operations of commutators, temperatures as high as 300 to 350 C. may be reached, for instance, when commutators are immersed in molten tin during the tinning operation- Thus mica plates and cones used in commutatonconstruction may be subjected to temperatures sufficiently high to cause the shellac to ooze out from the mica composition between the copper segments. At higher temperatures this escaped shellac when carbonized or decomposed may cause short circuits. When not actually carbonizedpartial decompositionof the shellac will yield decomposition products through destructive distillations which are deposited upon the various parts of the commutator and which are not only conductive in themselves but attack the copper and form additional deleterious non-insulating substances. Even when the shellac does not escape, its softening will cause sliding of the mica 40 plates when under pressure. In commutator construction, this displacement of the mica lates will leave the commutator bars loose.

t has been attempted'to overcome these difficulties by using a phenolic condensation product as a binder for composite mica articles but it was found this material would not adhere to mica with sufficient tenacity, nor bond mica lates together sufficiently well to form an a equately dense and strong insulation. Phenoliccondensation products also carbonize rather readily.

We have discovered that. esters of polythe bind molded articles with a polymerizable binder and in particular with a resin made from a polvhydric alcohol and a polybasic acid.

We prefer to use the reaction product of glycerine and phthalic anhydricl described in Callahan Patent 1,108,329 in the soluble, fusible condition characteristic of the first stage of the reaction. Conveniently the ester is applied as an acetone solution to the surface of the mica plates and is drawn in between the laps of the mica films by capillary force. In some cases we may build up the mica plates with dry mica flakes to the required thickness and introduce the binder solution between the laminae by immersing the plates in the solution and thus depend entirely on the capillary force to distribute In the manufacture of built-up mica articles as for example, commutator cones, a stack of sheet material is first made as above described. After evaporation of the acetone solvent this sheet material is heated in a press to a temperature of approximately 175 C. At this temperature reaction takes place in the glycerine ester, as described in the Patents No. 1,108,329 and No. 1,108,330, which if continued will result in the ester becoming hard, infusible and insoluble. As

it is not desired that the ester assume theinfusible state before the article of mica has been shaped, the heating is discontinued while the binder is still in an intermediate thermoplastic state. v

In this'condition the plate is subjected to machining operations to preform blanks or developed shapes of' the mica articles which we may desire to make. These developed f erize, the binder.

shapes are then formed and put into molds which have been heated to 250 (1., and at once put in a press which presses the micacuring and the higher temperatures for the final hardening operation. The molds are then taken out, again placed in a press and held under pressure until cooled off either by the natural loss of heat or by artificial cooling. In some cases articles not molded are subjected to a special heating treatment to cure same.

The resulting article is mechanically stronger than anarticle produced by the use of shellac as a binder, and there is no tendency forthe mica plates to slip over each other when the composite mica is subjected to high temperature nor for mica insulating parts, as tubes, to collapse under heat as will occur with shellac-pasted articles.

The binding or bonding material described is insoluble in water and mineral oil after it has been hardened by the. proper treatment under heat and pressure and 4 therefore the mica insulations produced with this material are'resistant to both water and mineral oils.

The electric insulating properties are superior to shellac pasted mica. Articles, produced in accordance with our invention may be subjected to the high temperatures encountered in the manufacture and operation of electric apparatus without deterioration or decomposition of binder.

For example, in some cases it is desired to subject such electric apparatus to the temperature of molten tin. It has been found that mica articles made as abovedescribed may be held in a tin bath at a temperature of 300- C. or even higher for six to seven. minutes without injury. At these high temperatures the glycerine resin or ester mstead 1 of becomin soft and letting go its hold upon the mica, tendsto become even harder and stronger if it has not already been converted into the final, infusible stage.

Although we have described the above s ific embodiment of our invention as app 'ed to composite mica articles in which mica scales are arranged to form distinct laminae, we wish that it be understood that v various modifications may be made within the scope of our invention. For example, mica powder or fine mica flakes may be mixed with a glycerine ester to form a meto heat an amass;

chanically strong,' "hard and tough material having valuable insulating properties.

this case the binder preferably, is mixed in a finely divided condition with the mica particles, the" proportions depending on the character desired in the final product. This mixture of owdered materials is subjected d pressure-to convert the resin into the hard, infusible state. The resin may be convertedto advantage partially to the final stage before comminutmg and. mixing with the mica powder thereby correspondingly shortening the time required for curing.

In'some cases the mixture of powdered mica and powdered resin may be compressed cold with or without a small quantity of solvent into the formof billets or slabs. These billets may be cut into blanks preparatory to pressingand finally pressed or molded at a temperature sufiiciently high to soften the binder.

While we have described our invention with particular reference to the utilization of a phthalic resin, we can utilize resins containing other polybasic acids, depending on the property desired of the product. For

example a more 'flexible product may be made using a malic acid resln, In a similar way resins may be used consisting of the reactlon product of a mixture of pol-ybasic acids and glycerine or other pol hydric alcohol or mixture of polyhydric a cohols.

What we claim as new and desire to secure by Letters Patent of the United States, is:

l 1. The process of makin moldedarticles which consists in applying to the materials to be molded a resinous, fusible ester of .a'

polybasic acid and a polyhydric alcohol, forming a blank of said composition, heating to a temperature snfliciently high to partiall polymerize said ester, fashioning said bla to desired form and continuin the polymerization of the'ester while mo ding under ressure.

2. e p] tions whic consists in coating mica ments with a resin comprising a compo b of a pol hydric alcohol and a polybasic acid in the i hsible'stage, forming blanks thererocess of making mica comipgsigund from, heating the same under pressure, thetemperature being sufliciently high to convert said resin to a partially polymerized condition, cutting 881d blanks to desired form and thereupon heating the formed product to further polymerize the resin.

3. The process 0 making composite articles which consists in applying to the materials to be sha a fumble resinous ester of hthalicanhy ids and glycerine, preformmg blanks from the resulting mixture under such conditions of temperature and time that said emr is partially converted to the nonfusible'condition, fashioning said blanks to shape, molding the product under pressure at a temperature at which further conversion of said ester occurs, and finally the product while under pressure.

mica which consists in applying a resin comprising a product of glycerine and phthalic anhydride toinica la-tes, forming blanks of desired thickness, eating the resulting product until i the resin is partially transformed to the infusible state, preforming the blanks and. then molding the same under heat and pressure.

5. The process of making articles comprising superimposed mica flakes which consists in applying to said superimposed flakes a polymerizable reaction product'of a polyhydric alcohol and a polybasic acid,

heating to partially harden said product, preforming the coated flakes and convertmg the product at a higher temperature and while under condition.

6. The recess of making mica sheet composition rom mica flakes which consists in building up plates from flake mica, together with a binder-comprising a compound of glycerine and phthalic anhydride, heating said plates under pressure to about 175 C. to partially polymerize said compound, heating said plates in a confined space to about 250 C, until the polymerization of the binder is complete and cooling said product to room temperature while under pressure.

40 I resinous product to the infusible state, shap- 7. The process-of making mica compositions from mica fragments which consists in applying a resinous reaction product of glycerine and phthalic anhydride in the fusible state to said fragments, forming blanks therefrom under pressure at a sufliciently high temperature to partially convert said ing said blanks into desired form, completing the conversion under pressure and finally cooling said product while under pressure.

8: The process of making composipressure to a hard, infusible complete the conversion 0 tions from mica flakes with a binder of a reaction product of glycerine and phthalic anhydride which consists in carrying out the forming of said materials while said binder is in a fusible state, hardening said'binder under pressure at a temperature of about 250 C. and finally cooling said material while under pressure.

9. The process of making mica compositions which consists in applying .to mica a fusible resinous condensation product of hthalic anh dride and glycerine, forming lanks theref i'om under such conditions of temperature and time that partial conversion of said condensation product to the infusible state occurs, fashioning said blanks to desired form, then moldin the formed, objectsat about 250 C., removing the molded objects from the mold and completing the conversion of the binder to the infusible state by heating said objectsat a temperature of about 300 C. 10. The process of making mica compositions which consists in mixing finely comminuted mica with a fusible polfyhydric-alcohol-polybasic acid resin in a; nely divided state, pressing the mixtu're to form blanks, shaping said blanks into desired form and finally molding at as'ufliciently high temperature to convert said resin to the infuslble state.

11. The process-of making mica composi owdered mica and polyhydric tions from alcohol-poly asic acid res' in wh1ch conslsts in --mi xing said resin with the mica 1n the owdered state while partially converted rom the fusible to the infusible state, forming blanks from said mixture, and finally molding at a sufliciently in h temperature to g the resin to the infusible state. a

In witness whereof, we have hereunto set our hands this 9th day of April, 1925.

LAWRENCE E. BARRINGER. CHARLES F. PETERSON. 

